The invention relates to an apparatus and to a method for controlling or regulating the deflection of micromechanically manufactured deflectable elements which, driven electrostatically, are deflected in an oscillating manner. Said elements can in particular be scanner mirrors which can be electrostatically excited to make a resonant vibration. A frequent function is the periodic deflection of a light beam. The invention specifically relates to an avoidance of the deflection restriction of the deflectable element by the so-called electrostatic pull-in effect.
Micromechanical, deflectable elements in many cases have a structure in accordance with FIG. 1. A deflectable element 1 in the form of a plate 1 is rotatably journaled via a torsion spring 2 within a frame element 5. Two counter-electrodes 3a and 3b can be located on a substrate 4 beneath the plate, as a deflectable element 1. If a potential difference of the electrical voltage is applied between the plate and one of the two counter-electrodes 3a or 3b, the plate is deflected in the direction of the respective counter-electrode.
The maximum usable deflection is restricted by the so-called pull-in effect. If the plate, as the deflectable element 1, approaches too closely to one of the counter-electrodes 3a or 3b, the electrostatic force exceeds the mechanical restoring force of the spring elements 2. The system becomes instable; the plate is accelerated toward the counter-electrode 3a or 3b and impacts there. This can result in the destruction of the plate, of the suspension or of the respective counter-electrode 3a or 3b. Due to this pull-in effect, only approximately ⅓ of the actually available distance can be utilized for a deflection—even in dynamic operation.
The maximum usable range for the deflection can only be somewhat increased by a specific design of the counter-electrodes.
With the usable range of the actually available distance restricted due to the pull-in effect, said distance must be comparatively large with a preset maximum deflection. However, this has the result that drive voltages of up to several hundred volts are required even in a dynamic case.
It is the object of the invention to provide a possibility with which a much larger deflection range can be utilized and in so doing the required voltage potential difference for the electrostatic drive of a deflection can be kept small and the occurrence of the pull-in effect can be avoided.
This object is solved in accordance with the invention by an apparatus having the features of claim 1. In this respect, it is possible to proceed in accordance with a method having the features of the claim.
Advantageous embodiments and further developments of the invention can be achieved using features designated in the subordinate claims.